W. N. Lennard

Characterization of Gd2 O 3 Films Deposited on Si(100) by Electron-Beam Evaporation

Gadolinium oxide films were deposited on Si(100) substrates from a rod-fed electron beam evaporator using a pressed-powder Gd 2 O 3 target. Films 25 nm thick were shown to he stoichiometric Gd 2 O 3 by Rutherford backscattering and had a dielectric constant at 100 kHz of 16.0 ± 0.3. Transmission electron microscopy and X-ray reflectivity measurements showed that films 7-13 nm thick annealed in oxygen consisted of three distinct layers, an interfacial silicon dioxide layer next to the substrate, a second amorphous oxide layer containing silicon, gadolinium, and oxygen above this, and a polycrystalline Gd 2 O 3 layer on top. Annealing in oxygen reduced the leakage currents, increased the thickness of the silicon dioxide layer, and increased the grain size of the top Gd 2 O 3 layer. The characteristics of the leakage currents through the gadolinium oxide were consistent with a Frenkel-Poole conduction mechanism with a silicon-Gd 2 O 3 band offset of 1.8 V. Interfaces with excellent electrical properties, Characteristic of good SiO 2 , were obtained after annealing in oxygen Annealing of the films in vacuum prior to oxygen annealing reduced the thickness of the interfacial silicon dioxide.

Absolute coverages for the various surface phases of CO and O adsorbed on Pd(110)

Abstract The absolute surface coverages of CO and O on Pd(110) have been measured by nuclear reaction analysis (NRA) using the 12 C(d, p) 13 C and 16 O(d, p 1 ) 17 O ∗ reactions. The CO coverages of the (2 × 1) and (4 × 2) phases of CO on Pd(110) are 1.00 ±0.05 and 0.73 ±0.05 ML (1 ML = 1 monolayer = 9.4 × 10 14 CO molecules cm −2 ) respectively. The oxygen coverage in the c(4 × 2) phase of O on Pd(110) is 0.50 ±0.05 ML.

Thermal stability and diffusion in gadolinium silicate gate dielectric films

Gadolinium silicate films on Si(100) annealed in oxygen and vacuum at temperatures up to 800u200a°C were analyzed by Rutherford backscattering and narrow resonance nuclear profiling. Oxygen diffused into the film eliminating oxygen vacancies, but Si diffusion, previously observed in Al and Y oxides and in La and Zr silicate films, was absent. Higher-temperature annealing in oxygen resulted in the formation of an interfacial layer observable in high-resolution electron micrographs. Gd0.23Si0.14O0.63 films crystallize at temperatures between 1000 and 1050u200a°C. These observations combined with recent electrical measurements show that gadolinium silicate films may be a good candidate for the replacement of SiO2 in deep submicron metal–oxide–semiconductor gates.

Structural properties of ultrathin arsenic‐doped layers in silicon

We have grown δ‐doped layers in Si by low‐energy As‐ion implantation during molecular beam epitaxy. The layers were investigated using cross‐sectional transmission electron microscopy, secondary‐ion mass spectrometry, Rutherford backscattering, and electrical measurements. The δ‐doped layers were between 3.5 and 5.5 nm thick, and showed perfect epitaxy with 50–80% of the incorporated As on substitutional sites. Layers doped at concentrations from 1×1013 cm−2 to 8×1013 cm−2 had bulk‐like mobilities and spanned the metal to insulator transition.

Atomic Layer Deposition of Hafnium Silicate Thin Films Using Tetrakis(diethylamido)hafnium and Tris(2-methyl-2-butoxy)silanol

Hafnium silicate films were grown by atomic layer deposition using the liquid precursors tetrakis(diethylamido)hafnium (TDEAH) and tris(2-methyl-2-butoxy)silanol, [CH 3 CH 2 C(CH 3 ) 2 O] 3 SiOH (TMBS). Using in situ ellipsometry, ex situ high resolution transmission electron microscopy (HRTEM), medium energy ion scattering (MEIS), and X-ray photoelectron spectroscopy (XPS), the details of the film thickness and composition were examined as functions of both the substrate temperature and silanol pulse time. Both HRTEM and MEIS measurements revealed that the films comprised two layers, with the surface layer containing more Hf than the layer in contact with the substrate. A self-limiting growth with a rate ~ 1ML/cycle was observed only after several initial cycles, a behavior that is ascribed to the chemistry of the initial Si substrate surface. Hf 4f XPS confirmed that the films were stoichiometric Hf x Si 1-x O 2 throughout despite the nonconstant Hf concentration with depth. A reaction mechanism between TDEAH and TMBS is proposed.

Depth profiling of ultrathin films using medium energy ion scattering

Abstract The medium energy ion scattering (MEIS) system at the University of Western Ontario has been modified by replacing the original one-dimensional position sensitive detector with a 2-D array. Calibration and analysis procedures for quantitative depth profiling are devised and established in this work: distortion correction, image tiling, charge state distribution of the scattered hydrogen ions, etc. The software to simultaneously control the sample manipulator (three orthogonal rotations), toroidal electrostatic analyzer and spectrum acquisition has been developed using LabView R . This development makes for easy sample alignment to the incident ion beam and automatically collects the step images. Additionally, the tiling procedure using corrected step images is accomplished within LabView R to produce a final energy–angle spectra. Our QUARK (quantitative analysis of Rutherford kinematics) spectrum simulation package has been modified to provide for non-linear least squares fitting to a measured MEIS energy spectrum. As a reference for quantitative analysis, a shallow Sb-implanted graphite sample was used with normalization to the height of the thick target carbon region by applying 1 H stopping power values from Konac et al. [Nucl. Instr. Meth. Phys. Res. B 136–138 (1998) 159]. To determine the system suitability for compositional analysis, Zr silicate films of thickness 2–7 nm on Si (1xa00xa00) substrates have been characterized by MEIS, RBS and NRA. The absolute areal densities of constituent elements are in good agreement (within 15%) among the three methods.

Ultrathin Zirconium Silicate Films Deposited on Si(100) Using Zr ( O i ­ Pr ) 2 ( thd ) 2 , Si ( O t ­ Bu ) 2 ( thd ) 2 , and Nitric Oxide

i-Pr)2(tetramethylheptanedione,thd) 2 , Si(O t -Bu)2(thd) 2 and nitric oxide in a pulse-mode metallorganic chemical-vapor deposition apparatus with a liquid injection source. High resolution transmission electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy ~XPS!, and medium energy ion scattering were employed to investigate the structure, surface roughness, chemical state, and composition of the films. The nitric oxide used as oxidizing gas, instead of O2 , not only reduced the thickness of the interfacial layer but also removed the carbon contamination effectively from the bulk of the films. The as-deposited Zr silicate films with a Si:Zr ratio of 1.3:1 were amorphous, with an amorphous interfacial layer 0.3-0.6 nm thick. After a spike anneal in oxygen and a 60 s nitrogen anneal at 850°C, these films remained amorphous throughout without phase separation, but the interfacial layer increased in thickness. No evidence of Zr-C and Zr-Si bonds were found in the films by XPS and carbon concentrations,0.1 atom %, the detection limit, were obtained. The hysteresis, fixed charge density, and leakage current determined from capacitance-voltage analysis improved significantly after postdeposition anneals at 850°C and the films exhibited promising characteristics for deep submicrometer metal-oxidesemiconductor devices.

Ion channeling analysis of a Si1−xGex(As)/Si strained layer

A strained layer of Si1−x Gex (As)/Si has been grown by molecular beam epitaxy (MBE) with the As dopant introduced by 1 keV ion implantation during growth. Analysis of the layer was made using secondary‐ion mass spectrometry (SIMS), Rutherford backscattering (RBS), and proton‐induced x‐ray emission (PIXE)/channeling, using 2 MeV H+ ions. The layer thickness (∼1.4 μm) and composition (x∼0.015; nAs ∼6×1018 cm−3) measurements by SIMS, RBS, and PIXE were in agreement. RBS, PIXE/channeling showed that the crystalline quality of the strained layer was equivalent to that of the Si substrate. The substitutional fraction (∼0.75) of the As dopant was determined by PIXE/channeling.

Study of astrophysically important resonant states in 30S using the 32S(p,t)30S reaction

A small fraction of presolar SiC grains is suggested to have been formed in the ejecta of classical novae. The Si isotopic abundances in such grains can be determined from the 29P(p,γ)30S reaction rate at nova temperatures. The Si isotopic abundances provide us with information on the nature of the probable white dwarf progenitor’s core, as well as the peak temperatures achieved during nova outbursts, and thus the nova nucleosynthetic path. The 29P(p,γ)30S reaction rate at nova temperatures is determined by two low‐lying 3+ and 2+ resonances above the proton threshold at 4399 keV in 30S. However, only one of these two states has only been observed very recently. We have studied the 30S nuclear structure via the 32S(p,t)30S reaction at 5 laboratory angles between 9° to 62°. We have observed 14 states, eleven of which are above the proton threshold, including two levels at 4692.7±4.5u2009keV and 4813.8±3.4u2009keV that are candidates for the 3+ and the previously “missing” 2+ state, respectively.